The present invention relates generally to apparatus for processing whole blood, and more specifically to blood fractionation apparatus for separating and collecting a desired blood component, such as plasma.
Various methods and apparatus have been developed for the continuous flow processing of whole blood, wherein whole blood is taken from a live donor, a desired blood component is separated and collected, a replacement fluid is added to the processed blood, and the processed blood is returned to the donor. Blood components typically collected using such processing include plasma (plasmapheresis), white blood cells (leukopheresis) and platelets (plateletpheresis).
Continuous flow blood processing apparatus may be of the centrifugal type, wherein the differing density of the collected blood component causes the component to congregate for collection at a particular radial distance in a centrifuge, or may be of the filter type, wherein the particle size of the collected component allows only that component to pass through a filter membrane into a collection chamber. Filter type apparatus is generally preferable for continuous flow plasmapheresis applications, since such apparatus does not require complex rotating machinery and is more compact and less costly to manufacture.
One form of filter which is particularly attractive for use in plasmapheresis apparatus utilizes a plurality of parallel microporous hollow fibers arranged side-by-side in the form of a bundle within a hollow cylinder. As whole blood is caused to flow through the fibers the plasma component passes through the walls of the fibers to the surrounding container, which forms a collection chamber from which the component is transported to a collection bag. A preferred construction and method of manufacture of such a hollow fiber filter is shown in the copending application of Robert Lee and William J. Schnell, entitled, "Microporous Hollow Fiber Membrane Assembly and its Method of Manufacture", Ser. No. 278,913, filed June 29, 1981. A preferred form of apparatus for use in conjunction with such a hollow fiber filter is shown in the application of Arnold C. Bilstad and John T. Foley, "Blood Fractionation Apparatus", Ser. No. 330,898, filed concurrently herewith and incorporated herein by reference.
To preclude the collection of too much of one blood component, such as plasma, from a donor, and consequent danger to the donor's health, it is highly desirable that the volume of the blood component collected be monitored and maintained within prescribed limits. Preferably, the volume of the component actually collected and the rate of plasma collection should at all times be displayed in a digital form clearly readable by the operator. Prior art plasmapheresis apparatus relied on the weight of the plasma collection container to provide indications of collected plasma volume and plasma collection rate. One such apparatus is shown and described in the copending application of Arnold C. Bilstad and John T. Foley, entitled, "Apparatus and Method for Weighing Material Being Collected", Ser. No. 140,111, filed Apr. 14, 1980.
One drawback of such prior-art weight-based systems has been the necessity of making mathematical calculations to determine collected volume. Furthermore, it has been necessary to initially obtain the tare weight of the collection container prior to each collection procedure. Moreover, with such systems it has been necessary to reinitiate the collected volume measurement procedure with each change of collection container. This is not only time consuming, but also introduces a potential for error in the volume and rate determinations.
The present invention overcomes these drawbacks by providing a system which automatically determines and displays the volume of a blood fraction collected in plasmapheresis and similar blood fractionation apparatus by analyzing incremental changes in collected plasma weight over successive time intervals. The volume collected is continuously displayed, without consideration of changes in tare weights or changing of the plasma collection container.
It is also desirable in plasmapheresis and other blood fractionation procedures that the rate of collection of the blood component be continuously displayed. This allows the fractionation apparatus to be adjusted for optimum performance, and provides an additional safety check on the operation of the apparatus. In prior art filter-type plasmapheresis systems the collection rate could only be determined by mathematical analysis of collected volumes of plasma over known time intervals. This procedure required an undue amount of time on the part of an operator, and was by its nature often not a sufficiently current indication by which operating adjustments to the apparatus could be made.
The plasmapheresis apparatus described herein incorporates a system wherein plasma collection rate is derived by accumulating and averaging incremental changes in plasma volume, as developed by the previously described volume display system, and is displayed in a clear and unambiguous digital format, allowing the rate display to be used for adjustment of the plasmapheresis apparatus. This system is described in detail in the application of Arnold C. Bilstad and John T. Foley, entitled, "Blood Fractionation Apparatus Having Collection Rate Display System", Ser. No. 330,901, filed concurrently herewith and incorporated herein by reference.
In plasmapheresis procedures it is frequently desirable that a replacement fluid be introduced into the processed plasma-deficient blood to replace the collected plasma prior to returning the processed blood to the donor. In this exchange procedure the replacement fluid is typically introduced by a replacement pump at a fixed volume ratio to the collected plasma, as specified by the attending physician.
In prior art filter-type plasmapheresis systems the speed of the replacement pump, and hence the replacement fluid rate, was manually set by the operator, after observing the plasma collection rate and mathematically calculating the necessary replacement rate from the specified replacement ratio. For each change in collection rate is was necessary to manually reset the replacement rate, and failure to note a change in collection rate resulted in an improper replacement rate.
The plasmapheresis apparatus illustrated herein incorporates a replacement ratio control system which provides an exchange mode wherein the volume of replacement fluid added to the volume of plasma actually collected is automatically proportioned according to an operator-set ratio. The system includes an autologous mode, wherein plasma is withdrawn from the collection container for treatment and return to the donor by the replacement pump at a rate which is automatically set to maintain a constant volume of collected plasma in the collection container. This control system is described in detail in the copending application of Arnold C. Bilstad and John T. Foley, entitled, "Blood Fractionation Apparatus Having Replacement Fluid Ratio Control System", Ser. No. 330,900, filed concurrently herewith and incorporated herein by reference.